We also emphasize that LLP searches are instrumental in the hunt for Dark Matter and are often the only way of observing the DM directly, as demonstrated by several recent studies [1]}, [2]}, [3]}, [4]}.
In models like Freeze-In DM (FIDM) [5]}, [1]}, inelastic DM (iDM) [7]}, [8]}, co-annihilating DM [2]} or co-scattering DM [3]}, the relic abundance of the stable DM candidate is determined by the properties of an LLP in the thermal plasma of the Big Bang.
This LLP carries the same quantum number which stabilizes DM, and decays into DM + SM final states.
The DM particle itself could be almost completely sterile, precluding a direct detection signal, and production of the parent LLP at colliders could then be the only way to produce and observe DM.
